Electric motors use electrical energy to produce mechanical energy. In conventional brushless DC motors, a controller (generally external to the motor) generates a control signal that is synchronized to the rotor's position. One or more permanent magnets are attached to an external rotor, and one or more Hall-effect sensors are used to sense the position of the rotor. The stator (e.g., the non-moving part of the motor) conventionally includes an armature including three phases of driving coils. The coils are activated by the controller in response to signals from the Hall-effect sensors. The changing current signals that are produced by the controller produce magnetic fields, which interact with the magnetic fields of the fixed magnets to cause the rotor to rotate with respect to the stator.
Electrical motors are used in a wide variety of applications. For example, leisure applications may include wheeled vehicles such as golf carts, neighborhood electrical vehicles (NEVs), electric bicycles and motorcycles. Smaller motors may be used by hobbyists in radio-controlled wheeled vehicles and aircraft. Industrial applications may include electrical burden and/or utility carriers and electric tow tractors. More advanced applications may include electric and/or hybrid vehicles, military scout vehicles, and unmanned aerial vehicles (UAVs), among others.
In general there is a desire to improve the overall efficiency of all types of electric motors (or generators). In particular, it is desirable to improve performance of an electric motor to achieve a higher power output with lower weight and smaller size. Conventional electric motors have reached certain limits. For example, it is well-accepted that an increased magnitude of current flowing through an armature will translate generally into increased torque and horsepower, all other factors being equal. However, the way conventional armatures are wound has limited the amount of copper that can be disposed in a magnetic field. This limits the amount of current that can be passed through the armature, and results in limited maximum torque and horsepower.
The amount of copper that can be disposed in a magnetic field may be limited by the paths taken by the conductor leads that supply current to each coil. This may be the case, for example, when the individual coils are wound on a plane that includes a thickness of only one winding, or stated in another way, when the thickness of each individual coil is equal to that of the lead (wire size). In such a coil, one coil lead (i.e., an outside lead) leading to or from the coil is disposed on the plane of the coil and a remaining coil lead (i.e., an inside lead) must pass over the coil to exit. The overall effective thickness of the coil then becomes the thickness of two wire diameters. The two-lead diameter effective thickness of each conventional dual layer type of coil thus separates the planes of adjoining parallel coils. The increased thickness of the coil increases the distance that the magnets above and below the coil layer(s) are disposed from each other. The magnetic field strength (i.e., magnetic flux) is thereby decreased, generally resulting in decreased torque and horsepower. This is especially true with axial field motors that have multiple wound coils that are arranged radially on a plane to form a planar radial coil assembly. When a plurality of the planar radial coil assemblies are located adjacent to each other to form a stator, the distance between the adjoining coils is increased by the thickness of the leads. Thus, it is desirable to arrange a plurality of coils on adjacent parallel planes and wire them either in series or in parallel to increase the electrical power that is passing through the coils and therefore the performance of the motor or generator.
Conventional mechanical constraints relating to coil lead ingress and egress have generally caused the individual coils of the planar radial coil assembly to be placed apart from each other radially (i.e. to have a greater arc spacing between the coil assemblies) and also for each planar radial coil assembly that is disposed apart from an adjoining planar radial coil assembly. Therefore, it is desirable to place the coils closer to each other radially and/or laterally. Other areas for improvement may include minimizing tolerances and therefore the spacing between the armature and the rotor magnets so as to further increase magnetic field strength. It may also be desirable to improve the shape of the coils and/or the effective or active area of the coils, improve a feedback signal of the rotor position as an input to a controller that supplies an electrical waveform to drive the motor, and/or increase the number of phases.
Still other areas in which improvement are desired include minimizing errant magnetic flux, providing a maximum amount of redundant components to drive down cost of manufacture, providing a versatile design that uses a standard single rotor and stator assembly for a basic motor (or generator) configuration that can be stacked longitudinally so as to increase the number of stator and rotor pairings using as many sections as desired to increase torque and horsepower to the desired degree, reducing the number of electrical leads inside the motor that can become intermittent or fail, improving motor longevity (life expectancy), improving motor cooling without adding fans or other parts that decrease efficiency, and especially improvements that minimize the size and weight of the motor.
Existing applications would benefit from such improvements and new applications are likely to arise. Minimizing the cost of manufacture of an improved axial field motor would further expand the desirability of such a motor.
For example, electric motor-powered aircraft—from radio controlled aircraft to human carrying ultra-light aircraft—stand to gain from such improvements. A generally accepted threshold for using electric motors to power hang gliders (or other types of ultra light aircraft) is a minimum of about 15 HP at about 2800 rotations-per-minute (RPM), where the motor weighs about one-half of the weight of the current most-efficient motor designs. Ideally, such a motor would also be economical so as to not preclude its use in many new or old applications.
Similarly for radio controlled aircraft, if a comparable performance electric motor is provided that is lighter in weight than its predecessor then, for any given combined weight of motor and batteries that a radio controlled model airplane can carry, additional batteries can be carried that equal the difference gained by reducing the weight of the motor. This directly translates into greater airtime and therefore greater performance and/or enjoyment for the user.
It is also desirable for certain applications to be able to eliminate the need for a gear box. This can save weight if the RPM of the output shaft is equal to that which is desired to drive the load. It also improves efficiency as all mechanical gear reduction or gear increase types of drives also consume power. Therefore, there remains a long-standing need to use motor design and especially motor diameter as a means of controlling RPM, thereby eliminating the need for a gearbox in certain applications. This would save additional weight, improve efficiency, and decrease the number of component parts that can fail.
In order to reduce costs, it is desirable to manufacture components that can be used in a variety of different configurations that produce different power, torque, or RPM outputs. For example, it is desirable to provide a design in which additional offset coil layers, or fields, may be stacked top of one other which may supply greater power and decrease ripple (e.g., with a phase delay for each layer).